1. Field of the Invention
The invention relates to a door closer based on a cam mechanism.
2. Description of the Related Art
Typically, door closers with a cam mechanism have a cam disc, which is torsion-resistantly disposed on an output shaft and has a running surface, on which a pressure roller rolls which is pressed against said surface by means of a closer spring.
The shape of the running surface determines the characteristics of the torque applied to the operated swing leaf during a closing movement, which is the torque curve resulting therefrom.
When seen in a longitudinal extension of the output shaft of the door closer, the cam disc may present a symmetrical or an asymmetrical form in cross-section.
The pressure roller is supported such that it can move towards and away from the cam disc. The movement takes place in the direction towards and away from the axis of rotation of the output shaft.
The torque curve is predetermined by the shape of the respective running surface of the cam disc. This means that the cam disc has to be specifically configured, i.e. manufactured for each individual application.
In a slide-channel operation, cam discs that have a symmetrically configured cross-section result in a torque curve different from a standard arm assembly or a scissor-arm assembly, both in magnitude and progression.
However, in order to be able to utilize one and the same door closer for both modes of operation, the torque curves need to be substantially consistent.
Asymmetrical cam discs have been developed for this purpose, the two running surface halves thereof being configured for respectively one mode of operation. The progression of the respective torque curve defined by the shape of the running surfaces can not be modified.
However, if a door provided with a door closer is to be equipped with a fire protection function, torques are only admissible within certain limits in a predetermined first range of an opening angle (approximately 0° to 4°) of a swing leaf and in a predetermined second range of an opening angle (approximately 88° to 92°) of the swing leaf. Moreover, over the entire range of the opening angle of the swing leaf, there is a minimum torque, which can not fall below a certain value.
The only known possibility for modifying the torque at the swing leaf are mechanisms for adapting the initial tension of the closer spring. In most cases, such mechanisms comprise an adjusting screw, by means of which the position of a closure spring abutment can be modified. Thereby, the magnitude of the torque can be modified in a substantially constant proportion. The shape of the torque curve remains unchanged.
In the event a torque is too high at an opening angle of 0°, that is with the swing leaf being closed, and a final torque, that is a torque at a maximum opening angle of 90° to 100° for example, is only slightly higher than a minimum admissible torque, an adjustment of the initial tension of the closure spring could in fact reduce the torque at an opening angle of 0°, but at the same time the final torque would fall below the admissible minimum torque. Thus, a conversion to a fire protection function would be impossible. Replacing a door closer by a completely new one leads to enormous cost